Airplanes 135 
has been reported as Sitka spruce, but the quantity is rela- 
tively small. Sitka spruce is a much larger tree and yields 
larger pieces of clear stock. 
During the war period experts searched the Adirondacks 
for air-plane spruce, as it was termed. These men worked at 
spruce operations, marking logs which they thought were of 
airplane quality. Generally the butt log only was chosen from 
the tree, as the next log above was often knotty. The logs had to 
be not only free from knots and other defects but straight- 
grained as well. The grain of a board generally shows, but it 
is an entirely different matter to tell whether a tree will cut 
clear boards as it stands on the stump. Straight-grained spruce 
trees can, however, be chosen with a high percentage of accu- 
racy after a considerable amount of practice and close inspec- - 
tion and a checking up of results. A study carried on in the 
Adirondacks during the war period shows that on the areas 
examined 52 per cent of the trees were straight-grained enough 
_to pass the airplane specifications; but, because of knot condi- 
tions, few trees under 14 inches in diameter were of value, and 
of these trees about one-third were defective from other causes. 
Consequently the amount of timber actually available for air- 
plane purposes in the Adirondacks is probably comparatively 
small. 
Spruce is used largely in the fuselage shell, wing beams, 
wing posts, cap strips, engine beds, struts, and all other beams. 
Ash is used to a large extent in longerons and in parts requir- 
ing toughness and elasticity. Mahogany is used largely for 
propellers in the form of built-up stock of several thicknesses, 
from which the propeller is carved. White pine, both eastern 
and western, is used mainly in ribs and webs. Douglas fir is 
substituted for spruce in beams. 
Mahogany is the only propeller wood reported in New York, 
but black walnut and oak are also desirable material. Experi- 
ence shows that stock for this use should be quarter-sawn. 
Propellers or “screws,” as they are called, are built up of lam- 
inations, each being sawed to size and carefully chosen so as to 
